By the 1700s artists started buying their paints, brushes, canvas, paper, varnish and other supplies from specialized art supply stores, instead of grinding and mixing their own paints and buying the rest from a variety of makers.
In England, one of the first art supply companies was Daler Rowney. They opened their doors in 1780. Lefranc & Bourgeois, in France, had started a few decades earlier. Winsor & Newton in the UK, Blockx in Belgium, and Schmincke in Germany did not get in the business until the 1800s.
Of course, thousands of art supply stores and small supply manufacturers opened and closed their doors between the 1700s and today.
Most of these suppliers stenciled the canvases and boards they supplied with their name. Sometimes they used a paper label or an ink stamp, or blind tooled their name in the stretchers.
We use whatever information is available to research where and when the art supply store was in business. We also check to see if this matches where the artist lived or traveled and matches the origin of his supplies as documented in his recorded works.
Where and when a canvas or academy board was manufactured or sold does not by itself demonstrate that a painting is authentic. But, it creates a positive presumption if it matches where the painter lived and matches what is already known about the art supplies.
Of course, many artists traveled, studied and lived abroad, sometimes for many years. Therefore, individual biographies have to be factored in.
In the case of paintings very little is known about when research begins. Art supply origin provides a starting point. More often than not, American art supplies were used by American painters and German art supplies by German artists and so on.
Stencils, stamps, and labels of art supply companies are an additional source of information and another building block in the process of authenticating paintings.